Hi, OP -
I am a former Russell Group STEM admissions tutor. I think you have a lot of good advice above so my main point will be different. But I will concur with @Needmoresleep that Economics programmes can vary widely in content. Also I echo her point that Economics is heavily Statistics based. Physics makes much richer use of Maths. How significant is this for DS?
Furthermore, our graduates do get desirable jobs in the financial sector and this is typical of good STEM graduates from excellent programmes who have proactively aimed for the financial sector during their studies. So if DS is interested in a financial career, the choice may not be all that significant.
I also note per PP that actuaries have fabulous job satisfaction (and career progession), at or very close to the top of the league tables decade after decade. I am not sure what an actuarial degree (perhaps a joint hons degree) entails but it is worth knowing about. However one can also enter the career from an Economics or STEM discipline.
Now, I am mainly writing in response to your comment that you cannot afford to send DS to university in America. A minority of excellent American universities offer substantial financial aid to international students.
At the extreme, several Ivy League schools including Harvard and Dartmouth have a policy that a family on an income of less than $100,000 never pays a cent, nor does the student take a loan (though they may be required to work a pretty good university job, eg in a library or academic department, for a few hours per week during term time). Above that threshold there is a contribution but the asset calculator does not include the primary home or pension pots and it takes account of family size. I created a fake profile at Harvard as a Continental applicant with a family income of $175,000 pa (!) and including travel and health ins, my family was only paying about $20,000 pa. That’s barely more than the total costs of a British university when the exchange rate is bad, and I was posing as a fairly rich girl.
Other universities and elite four year colleges - the latter is a concept we don’t have in the UK but I will summarise below - offer less comprehensive aid, but this board has contained a number of posts from mums pleasantly shocked by what they have found.
The Fulbright Foundation which encourages bilateral UK-US educational exchange (Wm Fulbright was a distinguished US senator) has a website containing a lot of detailed information about this.
The elite four year colleges are staffed by academics who are superbly qualified nut decided at some point (in STEM usually after a postdoc) to focus more on teaching than research. So they don’t have PhD programmes.
Students get much more attention from academics than at universities. They can do independent study, summer projects, etc. Examples include Amherst, Swarthmore, Reed, the five Claremont Colleges east of LA, Oberlin and many, many more. A mum about a year ago on this board said she had a DC at Oxbridge, one at an Ivy and one at one of these colleges. The college student had the best experience. Amongst PG tutors and large employers the colleges are very well recognised; I am not sure about small employers in the UK (‘yes’ in the US).
Please forgive the detail; I myself have taught only at large universities in the US and UK. But some of our strongest American doctoral students (in a superb School) were from four year colleges, and I wanted to make clear that the education is recognised to be as good as any.
Anyway, your DS has a relatively nice problem!